IC card having a mica capacitor

ABSTRACT

An IC card  10 A has a mica capacitor  5 , an antenna coil  2  and an IC chip  3  formed on an insulating substrate  1 , where the mica capacitor is composed of a mica film  6  and electrodes  7   a  and  7   b  formed on both sides of the mica film  6 . terminal of the electrode  7   b  on one side of the mica capacitor  5  is formed on the other side of the mica capacitor  5 , and this terminal and a terminal of the electrode  7   a  on the other side are connected on the insulating substrate  1  with the use of an anisotropic conductive adhesive  4 . Thus, an IC card can be manufactured at low cost, in which the resonance frequency is stabilized and the antenna characteristics are improved.

TECHICAL FIELD

The present invention relates to a contactless IC card for RFID (RadioFrequency Identification) or the like.

BACKGROUND ART

Data carrier systems have become widespread, in which an interrogatingdevice (reader/writer) contactlessly induces a voltage in the antennacoil of a responding device (contactless IC card) to send and receivesignals.

As shown in FIG. 16, the basic circuit elements of such a contactless ICcard are an IC chip and a resonance circuit that is composed of anantenna coil and a capacitor, so that a specific configuration is toarrange the antenna coil, the capacitor and the IC chip on a substrate.

Formerly, rings of thin metal wires that are wound in one plane wereused for the antenna coil, but recently, a conductive layer of copperfoil or the like that is laminated on one side of an insulatingsubstrate is etched into rings, which improves the antennacharacteristics and the mechanical strength and reduces the number ofparts to be assembled. Moreover, the insulating substrate on which theantenna coil is etched is used as the dielectric for the capacitor. Thatis to say, the antenna coil and the capacitor are formed by etching theconductive layer of a laminated board, in which conductive layers areformed on both sides of an insulating substrate.

In this case, a polyimide film is used for the insulating substrate.Furthermore, copper foil adhered with an adhesive, or a copper layerformed, for example, by sputtering is used for the conductive layer.

However, polyimide has a high water absorption rate and its dielectricconstant changes as it absorbs moisture, so that the capacitance of acapacitor with a polyimide film as a dielectric changes as it absorbsmoisture, and there is the problem that the resonance frequency of theIC card shifts.

In particular, laminated boards in which a polyimide film and a copperfoil are adhered to one another with an adhesive have the advantage thatthey can be obtained at lower cost than those in which a copper layer issputtered onto the polyimide film, but the resonance frequency of the ICcard becomes even more unstable, because the adhesive becomes anothercause of changes of the dielectric constant, in addition to thepolyimide film.

It is an object of the present invention to solve these problems of therelated art, and to provide an IC card with stable resonance frequencyand improved antenna characteristics, which can be manufactured at lowcost.

DISCLOSURE OF THE INVENTION

The inventors have found that using a mica capacitor having a mica filmas a dielectric stabilizes the resonance frequency of the IC card,because the water absorption rate of the mica film is very low, and thatputting the terminals of the electrodes on both sides of the mica filmtogether on one side by means of a through-hole, the mica capacitor canbe mounted at low cost and with high reliability on a substrate using ananisotropic conductive adhesive; and based on these findings, thepresent inventors have completed the present invention.

Thus, the present invention provides an IC card having a mica capacitor,an antenna coil and an IC chip formed on a substrate, the mica capacitorbeing made of a mica film and electrodes formed on both sides of themica film, wherein a terminal of the electrode on one side of the micacapacitor is formed on the other side of the mica capacitor, and thisterminal and a terminal of the electrode on the other side are connectedon the substrate by an anisotropic conductive adhesive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show a plane view and a cross-sectional view along x-xof an IC card in accordance with the present invention, respectively.

FIGS. 2A and 2B show a top view and a bottom view of a mica capacitor,respectively.

FIGS. 3A, 3B and 3C are a series of plane views showing themanufacturing steps for an IC card in accordance with the presentinvention, where FIG. 3A shows the forming of the antenna coil, FIG. 3Bshows the mounting of the IC chip, and FIG. 3C shows the mounting of themica capacitor.

FIG. 4 illustrates the step of layering the peelable paper and the outerfilm in the manufacturing process for the IC card of the presentinvention.

FIG. 5 is a diagram illustrating the manufacturing process of an ICcard.

FIGS. 6A, 6B and 6C show a plane view, a cross-sectional view along x-x,and a cross-sectional view along y-y of an IC card in accordance withthe present invention, respectively.

FIG. 7 is a plane view taken during the manufacturing process of the ICcard of the present invention, after the antenna coil has been formed.

FIGS. 8A and 8B show a top view and a bottom view of the mica capacitor,respectively.

FIGS. 9A, 9B and 9C shos a plane view, a cross-sectional view along x-x,and a cross-sectional view along y-y of an IC card in accordance withthe present invention, respectively.

FIG. 10 is a plane view taken during the manufacturing process of the ICcard of the present invention, after the antenna coil has been formed.

FIGS. 11A and 11B show a top view and a bottom view of the micacapacitor, respectively.

FIG. 12 is a cross-sectional view of an IC card in accordance with thepresent invention.

FIG. 13A shows a cross-sectional view of an IC card of the presentinvention, and FIGS. 13B and 13C illustrate how this IC card and aconventional IC card are peeled off after having been attached to anarticle.

FIG. 14 is a cross-sectional view of an IC card in accordance with thepresent invention.

FIG. 15 is a graph showing the resonance frequency as a function of timewhen an IC card of Example 1 is subjected to an endurance test at 60° C.and 90% humidity.

FIG. 16 is a diagram illustrating the basic circuit elements in an ICcard.

BEST MODE FOR CARRYING OUT THE INVENTION

The following is a detailed description of the present invention, withreference to the accompanying drawings. In the drawings, like numeralsare used to denote like or equivalent structural elements.

FIGS. 1A and 1B show a plane view and a cross-sectional view along x-xof an IC card 10A in accordance with the present invention,respectively, which is used by sticking it as a label with ID functionto video films or other articles. In FIG. 1A, the area enclosed by thebroken line shows a magnification of the vicinity of the terminals of amica capacitor 5. The area filled with dots is connected by ananisotropic conductive adhesive 4. FIGS. 2A and 2B show a top view and abottom view of the mica capacitor 5 used for this IC card 10A,respectively.

This IC card 10A includes an antenna coil 2, an IC chip 3, and a micacapacitor 5 mounted on an insulating substrate 1 made of an insulatingfilm, such as PET or polyimide, which are sealed by a sealing resin 11made of a thermosetting resin, such as an epoxy resin, or a hot-meltingresin, such as polyester. Moreover, an outer film 13 made of polyesterfor example is laminated on the sealing resin 11 on the side of theinsulating substrate 1, with a pressure-sensitive adhesive 12, made ofan acrylic resin or the like, arranged between the sealing resin 11 andthe outer film 13. A peelable paper 15 is laminated on the oppositeside, with a pressure-sensitive adhesive 14 arranged between the sealingresin 11 and the peelable paper 15. When using the IC card 10A as alabel, this peelable paper 15 can be peeled off, and the IC card 10A canbe tacked on certain articles with the pressure-sensitive adhesive 14.

In this IC card 10A, the antenna coil 2 is formed by etching a copperfoil laminated onto the insulating substrate 1. The IC chip 3 is mountedface down on the substrate 1 with the anisotropic conductive adhesive 4.

The mica capacitor 5 includes a mica film 6 and electrodes 7 a and 7 bformed on both sides of the mica film 6. In the drawings, a terminal 5 bof the electrode 7 b on the upper side of the mica film 6 is formed onthe lower side of the mica film 6 by means of a through-hole 9, andbrought together on the same side with the terminal 5 a of the electrode7 a on the lower side of the mica film 6. Consequently, the terminals 5a and 5 b of the mica capacitor 5 can be connected by the anisotropicconductive adhesive 4 with an inner terminal 2 a and an outer terminal 2b of the antenna coil 2, respectively.

The mica capacitor 5 is manufactured, for example, as follows. First, amica film 6 is prepared, which is provided with an aperture for thethrough-hole 9. Then, the electrode 7 b (or the electrode 7 a) is formedby silver paste printing on one side of the mica film 6. After that, thepattern for the electrode 7 a (or the electrode 7 b) and the terminal 5b of the electrode 7 b is also formed by silver paste printing. Thus,the aperture for the through-hole 9 is filled with silver paste, and thethrough-hole 9 electrically connects the electrode 7 b and its terminal5 b. Then, an insulating covering 8 of a glass coating or the like isformed on the side of the mica film 6, but leaving the terminals 5 a and5 b open.

Using this mica film 5, the IC card 10A is manufactured with the stepsillustrated in FIG. 5.

First of all, a laminated sheet (raw sheet covered with copper on oneside) in which a conductive layer of, for example, copper foil is formedon one side of an insulating substrate 1 made of an insulating film,such as PET or polyimide, is prepared, then this conductive layer iscoated with photoresist by one of the methods known in the art, and theantenna coil 2 and the accompanying circuit as shown in FIG. 3A areformed by exposing, developing and etching a predetermined pattern.Then, the IC chip 3 is mounted in a face-down fashion using theanisotropic conductive adhesive 4, as shown in FIG. 3B. Also the micacapacitor 5 is mounted using the anisotropic conductive adhesive 4.Then, the IC chip 3 and the mica capacitor 5 are bonded simultaneously.Thus, an antenna coil 2 is formed on the insulating substrate 1, asshown in FIG. 3C, and a mounting board on which the IC chip 3 and themica capacitor 5 are mounted is obtained. Here, one of the anisotropicconductive adhesives 4 known in the art can be used, and the anisotropicconductive adhesive 4 can be in the form of either a film or a paste,for example.

Then, as shown in FIG. 4, the outer film (label) 13 is tacked to themounting board on the side of the insulating substrate 1 with apressure-sensitive adhesive (not shown in the drawing), a sealing resin11 is applied to the other side, and a peelable paper 15 withpressure-sensitive adhesive is laid on top of the sealing resin 11 andlaminated to it while applying heat and pressure with a roller 16. Thus,the spacing between the outer film 13 and the peelable paper 15 can beadjusted to a predetermined gap width d. Then, after a stamping step, anarticle like the IC card 10A as shown in FIGS. 1A and 1B is obtained.

The resulting IC card 10A uses the mica film 6 as the dielectric for thecapacitor, so that there are no shifts in the resonant frequency due toabsorbed moisture, and the antenna characteristics are improved.Moreover, the mica capacitor 5 is mounted with the anisotropicconductive adhesive 4, so that the costs for mounting the capacitor canbe kept low, and the reliability of the adhesion is improved.

FIGS. 6A, 6B and 6C show a plane view, a cross-sectional view along x-x,and a cross-sectional view along y-y of an IC card 10B in anotherembodiment of the present invention, respectively. FIG. 7, which showsthe IC card 10B before the IC chip 3 and the mica capacitor 5 aremounted, is a plane view of the antenna coil 2 formed on the insulatingsubstrate 1. FIGS. 8A and 8B show a top view and a bottom view of themica capacitor 5 used for this IC card 10B, respectively.

Whereas the antenna coil 2 in the above-described IC card 10A issubstantially rectangular, the antenna coil 2 in this IC card 10B issubstantially circular. Thus, there is no particular limitation withregard to the shape of the antenna coil 2 in the present invention.

Also in this IC card 10B, the terminals of the electrodes on both sidesof the mica capacitor 5 are put together on one side of the mica film 6by means of the through-hole 9, so that it becomes possible to mount themica capacitor 5 on the insulating substrate 1 using the anisotropicconductive adhesive 4, but in this IC card 10B, the mica capacitor 5 isprovided with an additional terminal 5 a′ (see FIG. 8B). That is to say,as the terminal of the mica capacitor 5 for connecting to the outerterminal 2 b of the antenna coil 2, the terminal 5 a is formed on theelectrode 7 a on the lower side of the mica film 6, but the electrode 7a also has a terminal 5 a′ on the inner side of the antenna coil 2. Aterminal 2 b′ connected to the terminal 5 a′ is formed on the insulatingsubstrate 1, and this terminal 2 b′ is connected with a wiring patternto a terminal 2 b″, which is connected to a terminal 3 b of the IC chip3 (see FIG. 7). An insulating covering (not shown in the drawings) isformed on the side of this mica capacitor 5 as well, except for theterminal portions.

On the other hand, the inner terminal 2 a of the antenna coil 2 isconnected with the anisotropic conductive adhesive 4 to the terminal 5 bof the electrode 7 b on the upper side of the mica film 6, but theantenna coil 2 is also provided with an inner terminal 2 a′ forconnection with the terminal 3 a of the IC chip 3.

Consequently, in this IC card 10B, the outer terminal 2 b and the innerterminal 2 a of the antenna coil are respectively connected to theterminals 3 b and 3 a of the IC chip 3, so that it is not necessary toaccommodate the entire winding width of the antenna coil 2 between thetwo terminals 3 a and 3 b of the IC chip. Thus, the design freedom ofthe antenna coil 2 for this IC card 10B can be increased.

FIGS. 9A, 9B and 9C show a plane view, a cross-sectional view along x-x,and a cross-sectional view along y-y of yet another IC card 10C inaccordance with the present invention, respectively. FIG. 10, whichshows the IC card 10C before the IC chip 3 and the mica capacitor 5 aremounted, is a plane view of the antenna coil 2 formed on the insulatingsubstrate 1. FIGS. 11A and 11B show a top view and a bottom view of themica capacitor 5 used for this IC card 10C, respectively.

Like the above-described IC card 10B, this IC card 10C has asubstantially circular antenna coil 2. Also in this IC card 10C, theterminals of the electrodes on both sides of the mica capacitor 5 areput together on one side of the mica film 6, and connected on theinsulating substrate 1 using the anisotropic conductive adhesive 4.

Furthermore, in this IC card 10C, as the terminal of the mica capacitor5 for connection to the outer terminal 2 b of the antenna coil 2, theelectrode 7 b on the upper side of the mica film 6 is provided with aterminal 5 b that is connected to the terminal 2 b of the antenna coilby means of a through-hole 9, but the electrode 7 b also has a terminal5 b′ on the inner side of the antenna coil 2 (see FIG. 11A). Like in theabove-mentioned IC card 10B, a terminal 2 b′, which is connected to theterminal 5 b′, is formed on the insulating substrate 1, and thisterminal 2 b′ is connected with a wiring pattern to a terminal 2 b″,which is connected to a terminal 3 b of the IC chip 3 (see FIG. 10).

On the other hand, the inner terminal 2 a of the antenna coil 2 isconnected with the anisotropic conductive adhesive 4 to the terminal 5a, which is connected to the electrode 7 a on the lower side of the micafilm 6 by means of the through-hole 9. The antenna coil 2 is alsoprovided with an inner terminal 2 a′ for connection with the terminal 3a of the IC chip 3.

Consequently, also in this IC card 10C, it is not necessary toaccommodate the entire winding width of the antenna coil 2 between thetwo terminals 3 a and 3 b of the IC chip 3, and the design freedom ofthe antenna coil 2 can be increased.

Furthermore, in this IC card 10C, the electrode 7 a on the lower side ofthe mica film 6 is formed at a position where it does not overlap withthe antenna coil 2. That is to say, the region where the mica capacitor5 overlaps with the antenna coil 2 is a region in which only one side isprovided with an electrode (single-sided electrode region), and thisregion is made only of the mica film 6 and the electrode 7 b on theupper side. This single-sided electrode region intersects with theantenna coil 2 with the mica film 6 arranged on the side of the antennacoil 2. With this IC card 10C, the insulation between the antenna coil 2and the electrodes of the mica capacitor 5 can be ensured even when themica film 6 overlaps directly with the antenna coil 2. Consequently, itis possible to reduce the thickness of the mounting board on which themica capacitor 5 is mounted.

FIG. 12 is a cross-sectional view of an IC card 10D in yet anotherembodiment of the present invention. In this IC card 10D, just like inthe mounting board used for the IC card 10B shown in FIGS. 6A, 6B and6C, the antenna coil 2 is formed on the insulating substrate 1 of themounting board, and the IC chip 3 and the mica capacitor 5 are mountedon the mounting board, but instead of the sealing resin 11 and thepressure-sensitive adhesive 12 and 14 of the IC card 10B in FIGS. 6A, 6Band 6C, a pressure-sensitive adhesive 17 is used that also serves as afiller, and the peelable paper 15 is provided on its surface.Consequently, the thickness of this IC card 10D can be reduced to abouthalf the thickness of the IC card 10B in FIGS. 6A, 6B and 6C.

In order to prevent fraudulent reuse of the IC card, in which the ICcard is peeled off after it has been adhered to a certain article andthen attached to a different article, it is preferable that fraudulentlypeeling off the IC card once it has been tacked to a certain articledestroys the IC card.

When the card is made thinner like the IC card 10D in FIG. 12, thepeeling angle è₁, that is made when the IC card 10D is peeled off asshown in FIG. 13B after it has been tacked to a certain article S asshown in FIG. 13A, is larger than the peeling angle è₂ that is made whenthe IC card is thick (FIG. 13C). Consequently, when this IC card 10D ispeeled off the article, a large load is applied on the mounting plateinside the IC card, so that the mounting plate breaks easily. Thus, itis possible to prevent fraudulent reuse.

With regard to preventing fraudulent reuse of the IC card, it ispreferable to select a pressure-sensitive adhesive material 17 that hasgreater adhesion to the article S than to the mica capacitor 5. If thearticle S to which the IC card 10D is tacked is an ABS resin, thenexamples of suitable pressure-sensitive adhesive materials 17 includeUV-curing resin pressure-sensitive adhesives (such as G9000 by SonyChemicals, Corp.) and acrylic pressure-sensitive adhesives (such asT4000 and NP203 by Sony Chemicals, Corp.).

Thus, if the mica capacitor 5, the antenna coil 2 and the IC chip 3 onthe insulating substrate 1 are covered by a jacket material formed onthe pressure-sensitive adhesive material 17, and if thepressure-sensitive adhesive material 17 is provided directly at least onthe mica capacitor 5 without a sealing resin interposed between the two,and the thickness of the IC card 10D is reduced or the adhesion of thepressure-sensitive adhesive material 17 to the article S is increased,then once the IC card 10D has been tacked to the article S, the micacapacitor 5 is destroyed easily at the border between the electrodes 7 aor 7 b of the mica capacitor 5 and the mica film 6 when trying to peelthe IC card 10D off the article S, as indicated by the arrows A1 and A2in FIG. 12, and destruction of the mica capacitor 5 or the resonancecircuit also tends to occur from the position where the mica capacitor 5is connected to the insulating substrate 1 with the anisotropicconductive adhesive 4, as indicated by the arrow B.

The IC card 10E in FIG. 14 is provided with a jacket film 18 as a jacketmaterial replacing the outer film 13 and the peelable paper 15 of the ICcard 10D in FIG. 12. Whereas the above-described IC cards 10A, 10B, 10Cand 10D are tacked to an article by peeling off the peelable paper 15,this IC card 10E is not tacked to an article but used as an individualcard. Thus, it is preferable that also in this IC card 10E used as anindividual card, the pressure-sensitive adhesive 17 is provided directlyat least on the mica capacitor 5 without a sealing resin interposedbetween the two, so as to prevent the fraudulent use and tampering ofdata stored on the IC card 10E.

The IC card of the present invention is not limited to theabove-described IC cards 10A, 10B, 10C, 10D and 10E, and many variationsare possible. Consequently, it is not always necessary to use the outerfilm 13 or the peelable paper 15 with pressure-sensitive adhesive as thejacket material. Moreover, the shape and the position of the electrodesof the mica capacitor 5 and their terminals can be selected asappropriate.

EXAMPLE

The following example describes the present invention more specifically.

Example 1

An IC card as shown in FIG. 1 was manufactured according to thefollowing specifications:

insulating substrate: PET film (50 μm thickness)

raw material for antenna coil: copper of 35 μm film thickness

inductance of antenna coil: 0.92 μH

resistance of antenna coil: 0.6Ω

length of antenna coil: 418 mm

number of antenna coil windings: 4 turns

dielectric constant of mica film: ∈=7.1

capacitance of mica capacitor: 150 pF

IC chip: contactless IC (13.56 MHz)

outer film: polypropylene film

Evaluation

To evaluate the reliability of the IC card of Example 1, the IC card wassubjected to an endurance test at 60° C. and 90% humidity, and shifts inthe resonance frequency were determined. The results are shown in FIG.15.

The resonance frequency shifts in this Example 1 were suppressed toabout ⅓ of those in a conventional IC card using a polyimide film as theinsulating substrate.

INDUSTRIAL APPLICABILITY

With the IC card of the present invention, the resonance frequency canbe stabilized, because it uses a mica capacitor. Furthermore, themanufacturing costs can be lowered and the reliability of the connectioncan be improved, because the electrode terminals are put together on oneside of the mica capacitor, and the mica capacitor can be mounted withan anisotropic conductive adhesive.

What is claimed is:
 1. An IC card comprising a mica capacitor having asingle-sided electrode region formed on a portion of the mica capacitor,an antenna coil and an IC chip formed on a substrate, the mica capacitorcomprising a mica film and electrodes formed on both sides of the micafilm, wherein a terminal of an electrode on one side of the micacapacitor is formed on the other side of the mica capacitor, and theterminal of the electrode on the one side and a terminal of theelectrode on the other side are wirelessly connected on the substrate byan anisotropic conductive adhesive, and wherein the single-sidedelectrode region comprises one of the electrodes and the mica film. 2.The IC card according to claim 1, wherein the terminal of the electrodeon one side of the mica capacitor is formed on the other side of themica capacitor by means of a through-hole.
 3. The IC card according toclaim 2, wherein, in case where one terminal of one electrode of themica capacitor is connected to an outer terminal of the antenna coil,said electrode also has another terminal on an inner side of the antennacoil. substrate by an anisotropic conductive adhesive, and wherein thesingle-sided electrode region comprises one of the electrodes and themica film.
 4. The IC card according to claim 2, wherein the single-sidedelectrode region intersects with the antenna coil with the mica filmarranged on a side of the antenna coil.
 5. The IC card according toclaim 2, wherein the mica capacitor, the antenna coil and the IC chip onthe substrate are covered by a jacket material with anpressure-sensitive adhesive material interposed therebetween, andwherein at least on the mica capacitor, the pressure-sensitive adhesivematerial is provided without an interposed sealing resin.
 6. The IC cardaccording to claim 1, wherein, in case where one terminal of oneelectrode of the mica capacitor is connected to an outer terminal of theantenna coil, said electrode also has another terminal on an inner sideof the antenna coil.
 7. The IC card according to claim 6, wherein thesingle-sided electrode region intersects with the antenna coil with themica film arranged on a side of the antenna coil.
 8. The IC cardaccording to claim 6, wherein the mica capacitor, the antenna coil andthe IC chip on the substrate are covered by a jacket material with anpressure-sensitive adhesive material interposed therebetween, andwherein at least on the mica capacitor, the pressure-sensitive adhesivematerial is provided without an interposed sealing resin.
 9. The IC cardaccording to claim 1, wherein the mica capacitor, the antenna coil andthe IC chip on the substrate are covered by a jacket material with anpressure-sensitive adhesive material interposed therebetween, andwherein at least on the mica capacitor, the pressure-sensitive adhesivematerial is provided without an interposed sealing resin.
 10. The ICcard according to claim 1, wherein the single-sided electrode regionintersects with the antenna coil with the mica film arranged on a sideof the antenna coil.
 11. The IC card according to claim 10, wherein themica capacitor, the antenna coil and the IC chip on the substrate arecovered by a jacket material with an pressure-sensitive adhesivematerial interposed therebetween, and wherein at least on the micacapacitor, the pressure-sensitive adhesive material is provided withoutan interposed sealing resin.
 12. A mica capacitor for an IC card havinga substrate, the mica capacitor having a single-sided electrode regionformed on a portion of the mica capacitor, the mica capacitor comprisinga mica film and electrodes formed on both sides of the mica film,wherein a terminal of an electrode on one side of the mica capacitor isformed on the other side of the mica capacitor, and the terminal of theelectrode on the one side and a terminal of the electrode on the otherside are wirelessly connected on the substrate by an anisotropicconductive adhesive, and wherein the single-sided electrode regioncomprises one of the electrodes and the mica film.